Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$45.54	10.122%	$50.1496	$50.15	$50.15	$50.10
Purchase #2	$143.56	5.183%	$151.0007	$151.00	$151.00	$151.00
Purchase #3	$14.45	6.489%	$15.3877	$15.39	$15.40	$15.40
Purchase #4	$76.72	6.335%	$81.5802	$81.58	$81.60	$81.60
Purchase #5	$198.28	8.655%	$215.4411	$215.44	$215.45	$215.40
Purchase #6	$115.96	13.251%	$131.3259	$131.33	$131.35	$131.30
Purchase #7	$52.73	13.160%	$59.6693	$59.67	$59.65	$59.70
7 purchase totals =	$647.24		$704.5545	$704.56	$704.60	$704.50